Grinding machine



Jan. 19, 1943. 1 P. R. HOFFMAN 2,308,512

GRINDING MACHINE Filed Dec. 6, 1941 2 Sheets-Sheet l [34 a V I /a /6 ll20 e0 6 60 Jan. 19, 1943. P. R. HOFFMAN f3 2,308,512

GRINDING uAcIiIm-f Filed Dec. 6, 1941 isheets-sheet 2 Philip R. Hoffmdnzmethod and means.

7 other objects of the vention is disclin Patented Jan. 19, 1943 PhilipB. Hoflman, Car, Pa Grover C. Hunt, Carlisle, Pa

' Application December 0, 1941, Serial No. 421,999

This invention relates to grinding machines of the type generally knownas lapping machines and, more specifically, relates to lapping machineswhich are particularly intended for the grinding of polygonal,relatively thin devices or articles such as piezo-electric crystals.

It has heretofore been proposed, and is now known, to provide a lappingmachine in which externally geared, disc-like work holders aredisposedbetween two superposed abrasive discs and are geared to an innerrotating pinion which is located centrally of the discs and to a ringgear which surrounds and is concentric with the pinion, either thepinion or the ring gear being rotated to cause the work holders todescribe a planetary movement about the centers of the discs and,simultaneously, to rotate about their respective axes. The articlescarried by the work holders are thus caused to move in either anepicycloidal or hypocycloidai path across the faces of the discs.

It is an object of the invention to provide a in a lapping machine ofthe type in which the work holders move in a planetary path andsimultaneously rotate about their respective centers, to cause thearticles being ground to follow a non-cycloidal path in which they willbe swept circumferentially of the discs throughout their movement,thereby providing an improved grinding action. It is also an object ofthe invention to provide a machine which is particularly useful andadvantageous in the diilicult and exacting work of grindingpiezo-electric crystals.

Means for effecting these objects, as well as invention, will be madeapparent by the following description and the annexed drawings, it beingunderstood that the description and drawings are only illustrative ofthe invention, for the limits of which reference must be had to theappended claims.

Referring to the drawings, in which the same reference numerals andletters refer to like parts,

Pig. 1 is a vertical sectional view of a machine according to myinvention, taken on line ii of Fig. 2 is a plan view of the machine of1, taken on line 2-2 of 1, and 1 Fig. 3 is a schematic view of one ofthe discs. showing the typical path of an article being ground when myinvention is employed. a thefeaturesofmyin- A machine the Thus, as shownin Fig. 1, the machine comprises a base or pulley and belt arrangement22.

standard 2 which supports a lower abrasive disc 4 adapted to bereceivedwithin which is fixed against movement, as by rigid at tachmentto the base. The lower disc is provided with a preferably circularcentral opening within which is disposed a pinion gear 6 which may bedriven by any suitable" means such as the pulley and belt 8. The geardextends substantially above the upper surface of the lower disc.Surrounding the disc 4 is a ring gear i0 which is provided with internaland external teeth I2, II respectively, it being noted that the piniongear 8 and ring gear Iii are concentric. The ring gear I0 is mounted forrotation and is supported by bearings l6 which engage the lower surfaceof an annular flange or cover 18 which is connected to the upper surfaceof the ring gear. A driving gear 20 engages the external gear teeth ringgear l0 and, in order to rotate the ring gear, may be driven by suitablemeans such as the An upper abrasive disc 80, which is substantiallyidentical with the iowerdisc is attached to a cover 32 and is the ringgear, whereby the abrasive faces of the two discs are opposed and willbe in engagement with each other unless the crystals or the work holdingmeans which are described hereinafter are interposed between them. Thecover 82 is provided with openings within which a fixed pin, such as N,may be received in order to prevent rotary or other movement of theupper disc. The cover may also be provided with handles 38 whereby itand the attached upper disc may be lifted. The upper disc and the covertherefor provided with a central opening the upper portion of the piniongear 6. Between the two so each of which is provided with gear teeth onits external periphery and is of such size that the those on the pinion.gear I and the internal teeth l2 of the ring gear. Openings 8: areprovided in each work holder, within which the crystals are received andheld during movement of the work holders.

In accordance with my invention, the pinion By reason of the rotation ofboth gears in'the. same direction and at different speeds the workholders will move in such a way that a crystal M of the discs areprovided circular work holders over the faces of the discs, by reason ofthe fact that the slower rotation of the ring gear in the "produced byrotation of the pinion gear and the rin gear at the specific speedsmentioned hereinbei'ore. By reason of this movement the grinding actionon the crystals is improved and the wear on the abrasive surfaces ismade more uniform.

It will be seen, by reference path followed by a crystal when ground ina machine constructed and operated in accordance with this inventioniollows long, sweeping, overlapping lines having large circumferentialcomponents. The radial travel from the outermost periphery to theinnermost periphery, as between points a and b in the direction of thearrow, requires a travel of almost one-half of the circumference of thediscs. Thes: lines of travel, overlapping as shown in Fig. 3 cause theentire faces tom.s,tnsttne of the discs to be traversed by the crystalsbeing ground, thus causing completely even wear of the surfaces of thediscs, whereby the character of the grinding is improved and the life ofthe discs prolonged.

While I have described my invention with refer-' ence to the grinding ofcrystals, it will be understood that the invention is of generalapplication and is not limited to the grinding of any particularmaterials or devices. It will also be understood that while I havedescribed my invention with reference to a machine having flxed,-

horizontal, vertically-spaced abrasives, it may without departing in anyway from the invention be applied to other types and constructionsofgrinding machines.

Although only one form of the invention is illusthis application, itwill.

trated and described in be understood by those skilled in the art thatmodifications and improvements 'may be made without departing in any wayfrom the spirit or scope of the invention. for the limits of whichreference must be had to the appended claims.

Iclaim:

1. A lapping machine comprising a pair of opposed abrasive discs, apinion gear at the center of said discs, 9. ring gear concentric withsaid pinion gear and surrounding said discs, a plurality of externallygeared work holders between said discs and arranged in a series aboutthe pinion gear and being geared to said pinion and ring gear, and meansfor rotating both said pinion gear and ring gear.

2. A lapping machine comprising a pair of opposed abrasive discs, apinion gear at the center of said discs, a ring gear concentric withsaid pinion gear and surrounding said discs. a pinrality of externallygeared work holders between said discs and arranged in a series aboutthe pinion gear and being geared to said pinion gear and ring gear,means for rotating the pinion gear.

and means for rotating the ring gear at a speed in R. P. M. less thanthat or the pinion gear.

3. A lapping machine comprising a pair of opposed abrasive discs, apinion gear at the center of said discs, an internal ring gearconcentric with said pinion gear and surrounding said discs, a pluralityof externally geared work holders between said discs and arranged in aseries about the.pinion gear and being geared to said pinion gear andring gear, and means for rotating both the pinion gear and the ring gearat diiierent speeds in R. P. M. v

4. In the grinding or articles by machines of the type comprising twoopposed abrasive discs, a pinion gear disposed at the center of thediscs, a ring gear disposed concentrically or the pinion gear andsurroundingthe discs, and a work holder disposed between the discs andhaving external gear teeth meshing with those of the pinion gear and thering gear, the method of causing articles held by the work holder tomove over the discs which consists in rotating the pinion gear androtating the ring gear at a speed in R. P. M. which is less than that orthe pinion gear.

PHILIP R. mm.

